Network Services Networking for Home & Small Business

Introduction Everyday we communicate across the Internet –What kinds of activities? What’s in common with all of these? –Servers All these interactions use standards & protocols

Client-Server Web Page Request –Client has web client software Browser- widely used client software –Server Host running an application that provides info or services to a client

Client-Server Web Site domain names to IP address translation Remote login to device to control it Send/Receive Assigns IP addresses Web SiteFile Transfer

Activity Complete

Standardized Communication Different computers & operating systems across the Internet –Communication not possible if they didn’t share a protocol Phone call China to US –We have connectivity –A Chinese sales person couldn’t be understood by an English speaking person –That’s why there’s protocols (rules) to follow

Licklider DoD Saw the need for networked computers 3 bidders w/ different systems –They couldn’t communicate with each other –Came up with the idea of ARPAnet, which later became the Internet

Client Server Interaction A web server & client use specific protocols and standards in exchanging info to ensure that the messages are received & understood. Application, transport, Internetwork and network access protocols

Client Server Interaction Application Protocol HTTP –Rules for how browser & web server interact You request web page Another protocol delivers it

Client Server Interaction Transport Protocol TCP –Manages the conversations/packet exchange –Splits message into segments –Flow control & acknowledgments between the hosts –Retransmission

Client Server Interaction Internetwork Protocol IP –Assigns IP addresses –Encapsulate into packets for routing

Client Server Interaction Network Access Protocols –Get on the Ethernet cable!!! Data Link Management –Takes packets & encaps them into frames –MAC addresses are attached here Physical Transmission –How bits go on media (wired, wireless)

Overview

Review Which server… –Translates names to IP addresses? –Used for remote login? –Assigns IP addresses? Which protocol… –Splits data into segments? –Controls flow of data? –Acknowledges receipt of data? –Requests retransmission if a piece is missing?

Review Which protocol adds the IP addresses? Which category of protocols encapsulates packets into frames? Which protocol is for the rules of how a browser & web server communicate? End of Day One

Transport Protocols IP addresses & routes data for all protocols Different applications use different protocols for transport of the data –How data is sent/exchanged TCP or UDP

Transmission Control Protocol Used when an application requires an acknowledgement –Like a registered letter in the mail Breaks messages into small numbered segments –If sender doesn’t get an ACK of message received, it retransmits –Only portion lost is resent On receiving host, TCP reassembles data FTP & HTTP are examples of protocols using TCP Look at Example

User Datagram Protocol Used for faster transmissions “Best effort delivery” –Standard postal letter No ACK or retransmission Used for streaming audio or video, Internet radio, VoIP

UDP & Internet Radio If some of the message is lost, it is not retransmitted. –You might hear a slight break in the sound. If TCP were used and the lost packets were resent, the transmission would pause to receive them and the disruption would be more noticeable.

Comparing TCP & UDP TCP –Slower –Segments –Acknowledgements –Retransmission –Reassembles –Connection- oriented UDP –Faster –Best effort delivery –No acknowledgements –No retransmit –Connectionless

Review

Port Numbers & Communication When message is delivered, port # assigned Used to keep track of conversations and destination services requested Each message sent, has a source & destination port number

Port Numbers, Communication & Sockets source & destination IP source & destination port numberThe combo of the source & destination IP AND the source & destination port number is known as a socket. –Used to identify the server and service being requested by the client. –Thousands of requests per day are tracked by this

Port Numbers Destination- tells about service requested –80- HTTP –25- SMTP –53- DNS –21- FTP –23- Telnet Source Port –Random –Allows multiple conversations

Domain Name Service Server with table of IP & host names Request sent to port 53 (DNS) –DNS server looks in table to translate it –If there, it lets client know –If not there, forwards to another DNS server If no learn, time out

Lab DNS Lab

Review What does represent? –An IP address Which server would translate that name to an IP address? –DNS server Which server would assign IP addresses? –DHCP server Which Application protocol does FTP use? –TCP

Review Why would an application use UDP? –No disruption if dropped packets (fast) –Slight interruption, but it keeps going Which protocol is used for web sites? –HTTP Which port # is… –FTP 21 –HTTP 80

Web Communication You want DNS gets you the IP address of it Your browser uses that IP & port 80 to request the web page Socket connection made with server Web page comes back to your browser encoded in HTML

Web Clients & Servers HTTP is not secure Secure HTTP ( is port 443

Lab Packet Tracer

FTP Clients & Servers Transfer files from host to host Built in to OS & browsers Also GUI based software available Client/Server Uses TCP Request to server on port 21 Port 20 to send files to client

FTP Up/downloading of files, music, web site

server receives & stores s You client allows access to view messages Protocols used in include SMTP, POP3, IMAP4

Protocols- SMTP SMTP (25) –Used to send from client to server – server to server

Protocols- POP3 POP3 (110) –Used to send client messages & deleted from storage on the server Mail on server until collected from client

Protocols- IMAP4 IMAP4 (143) –Like POP3, but it keeps messages on server until user deleted them

Configuring

IM Protocols: Clients & Servers Real-time communication Each IM service may use different protocols & destination ports –So you must have compatible IM software

Voice Protocols: Clients & Servers VoIP Can call similar clients –Calls to landlines need public phone network

More About Port Numbers ,535 Well-known ports – –Common applications Registered ports – ,151 –Can be source or destination ports –Used for specific applications like IM Private ports –49,152 & above –For source ports

Port # Review

Review Which service protocol… –Is used to send mail to server? SMTP –Is used to get mail from the server & keep it there until deleted? IMAP4 –Is used to communicate from server to server? SMTP –Is used to get mail from the server & delete it? POP3

Protocol Interaction They interact with each other –Protocol Stack Some protocols focus on content of message Others focus on moving the data Protocols visualized in layers

TCP/IP Model

Sending a Message Web Server to client (you) –Application data broken into TCP segments Each segment has a header w/ source & dest ports –Segment encapsulates HTTP & HTML data –Encapsulates into a packet w/ IP header IP header has source & dest IP addresses –IP Packet sent to Ethernet protocol Encapsulates into frame header & trailer Source & destination MAC AND error checking –Bits encoded onto the media

Sending

Receiving a Message Last process in reverse –Bits received by NIC & decoded Destination MAC recognized –Ethernet header & trailer removed Source & dest MAC removed –IP header removed Source & dest IP removed –TCP header removed Source & dest ports removed –Web page data passed to HTTP & browser –TCP segment received, reassembled, & page displays

Receiving

TCP/IP Model Match

OSI Model Primary model for protocol development Unlike TCP/IP model, this is for all protocols

Activity or TCP or UDP 01-5A-FF DC DHCP or POP3 or HTTP

Activity Handout Packet Tracer

Review

Network Services Networking for Home & Small Business